In conventional rectifiers and, more particularly, in a rectifier that is always subjected to vibration during equipped in a vehicle, the outer diameter of a columnar heat sink of a rectifying element is made larger than the inner diameter of a press-fit hole formed in a heat dissipation heat sink and a press-fit allowance is set so as not to drop the rectifying element from the heat dissipation heat sink after being press-fitted and attached. In this case, a high load is applied to the bottom outer surface, which serves as a pressing surface, of the columnar heat sink of the rectifying element; and accordingly, a problem exists in that a semiconductor pellet equipped on the bottom inner surface of the columnar heat sink deforms.
The following is included in conceivable techniques as countermeasures against the aforementioned problem.
1. A configuration is made such that the inner diameter of a press-fit hole is decreased gradually in a press-fit direction (from one side to the other side), a (cylindrical or columnar) heat sink of a diode is made to deform obliquely (conically) along the inner peripheral surface of the press-fit hole (Patent Document 1, FIG. 3), and press-fit is performed by uniformly applying a load to a pressing surface by a press-fit rod whose end surface is flat. Alternatively, the end surface of a press-fit jig is formed into a spherical concave surface and is mainly brought into contact with an outer peripheral portion of the pressing surface to suppress deformation of a rectifying element.2. Taper of a press-fit hole on the receiving side of a diode is set to 0.2 to 2.5 degrees, preferably 0.3 to 2 degrees; and thus, the diode is bonded without exceeding a maximum allowable press-fit force (Patent Document 2, FIG. 2). Knurling on the outer periphery of the diode deforms at a significantly large depth on the small diameter side of the press-fit hole on the receiving side of the diode. A press-fit process is controlled by taking into account the degree of offset and pressing force.3. The inner peripheral surface of a press-fit hole of a heat dissipation fin is formed in a tapered shape; and the inner diameter on the press-fit start side is made larger than the inner diameter on the opposite press-fit start side (Patent Document 3, FIG. 5). Alternatively, a configuration is made such that the inner diameter of the press-fit hole of the heat dissipation fin is constant and the outer diameter of the outer peripheral surface on the driving start side of a rectifying element is smaller than that on the opposite driving side, the outer peripheral surface being formed with knurling (Patent Document 3, FIG. 3). This prevents a deterioration in heat dissipation property caused by a reduction in contact area due to galling or the like on the press-fit start side and a deterioration in the life of thermal fatigue of the element. In FIG. 3 of Patent Document 3, concurrently with the before-mention, the opposite driving side is made lower than the driving start side in the radial height of a large diameter convex portion of the knurling shape, and the large diameter convex portion is well-fitted and driven to the heat dissipation fin while being further deformed in driving (start).4. A configuration is made such that a receiving hole is formed in an aluminum plate member with approximately a thickness of 6 mm by a punching die, and a diode is press-fitted. A contact range between the diode and the aluminum plate member is relatively small (Patent Document 4, FIG. 6). The punched member can be recycled in normal circumstances.
On the other hand, Patent Document 5 discloses a technique in which a member to be press-fitted and a press-fit member are held in sandwiched relation by an upper pressing portion and a lower pressing portion; and the lower pressing portion is brought into contact with the press-fit member from the lower side and is made to move upward to press-fit the press-fit member into the member to be press-fitted. A configuration is made such that, in order to improve the positioning accuracy of the member to be press-fitted, a centering pin whose outer peripheral surface is formed in a tapered shape is provided on the upper pressing portion and the centering pin is made to engage with a press-fit hole of the member to be press-fitted.